Drugs and medications administered by injection, as with a hypodermic needle and syringe, are often comprised of constituents that if mixed together and stored for a long period of time tend to degrade in one manner or another. Degradation can also occur to medications when they are stored in their fully diluted state for long periods. For these reasons medication constituents are typically mixed just prior to injection as by, for example, drawing them into a syringe from sealed vials. Sometimes, however, a phenomenon known as "blowback" occurs when a hypodermic needle is injected into or removed from such a vial whereupon some of the medication squirts free to ambiance. Blowback creates a dangerous situation since many drugs, though safe and effective when used internally as prescribed, are hazardous to external skin and to facial features such as the eyes. Indeed, many such drugs are carcinogenic or antineoplastic. Even some antibiotics and antimicrobials can be harmful. Blowback is also a hazard in the administration of a single drug since such is normally stored in a sealed vial, rather than within a syringe, which seal must be pierced in withdrawing the drug from the vial into the syringe.
To overcome these problems and others, mixing syringes have recently been developed as exemplified by those disclosed in U.S. Pat. Nos. 3,351,058, 3,380,451, 3,684,136, 3,881,485, 4,059,109, 4,159,109, 4,226,236 and 4,306,554. Though some of these syringes have tended to alleviate the problem of blowback, they have not been problem-free. For example, they are often designed so that they are easily activated by external pressure such as by finger pressure applied to a flexible housing as in a pinching motion or by accidental movement of their externally accessible plunger. Other mixing syringes, which are provided with frangible diaphragms that are pierced by the action of an internal needle in order to provide fluid communication between independent chambers, may also be easily actuated prematurely. Still others, which are provided with pressure operable flaps, are also susceptible to being prematurely operated and to having their contents be poorly mixed. In addition, in cases where medication constituents are housed within a frangible bulb within a syringe barrel, which bulb is crushed to establish fluid communication for mixing, there is the risk that some of the bulbous fragments may be ejected from the mixing syringe. This is also the case with the previously mentioned syringes that have frangible diaphragms. Many of these prior art syringes must also be made of plastic for flexibility, which is disadvantageous in cases where a drug to be administered therewith has a plasticizer that can leach into the plastic syringe material.
It thus is seen that syringe and vial systems and mixing syringes of the prior art have had distinct problems and limitations. Accordingly, the present invention seeks to provide apparatus which tends to alleviate these problems.